夸克数密度敏感性的格点研究

应用格点QCD理论对电荷涨落和夸克数密度敏感性进行了研究. 研究选取了 两个轻味夸克, 应用staggered作用量, 并选取了16×8²×4格点. 对电荷涨落和夸克数密度敏感性在V=(2a)³～(8a)³(这里a=\kou\dfrac{1}{4T})区间进行了数值计算. 结果显示, 在相变温度以下的区域内, 上述参数对体积V具有依赖性, 这表明了可以通过对上述参数的研究来确定强子的尺度. 在高于相变温度的区域内, 对体积V没有表现出依赖性.     

From QCD to Quark Potential Model

The connection between phenomenological parameters in the quark potential model and fundamental QCD parameters is established by studying the fermionic three-point Green's functions in QCD incorporating the effects of nonperturbative vacuum. The scale of chiralsymmetry-breaking leading to the constituent quark picture is estimated.     

Quark confinement and vortices in massive gauge-invariant QCD

Massive gauge-invariant QCD can support vortices (analogous to Nielsen-Olesen strings) of nearly finite classical action per unit area (there is a logarithmic short-distance singularity which is of little consequence). These vortices lead, in analogy to Abelian lattice-gauge theories, to confinement of fractionally charged quarks and color screening for gluons. In this paper, we make some qualitative remarks about the (Minkowski-space) dynamics which follows from this sort of confinement, studying not only $\text{q}\text{q}$ processes but also qqq processes. For the latter, the effective long-range vortex-induced interaction is approximately described as a sum of two-body potentials each of half the strength of the $\text{q}\text{q}$ potential (just as for the asymptotically free short-distance potentials), and linearly rising non-relativistically. There is an essential two-dimensionality about the confinement process which suppresses what would be the transverse degrees of freedom of strings joining quarks. A fully relativistic dynamics is given which is amenable to a simple phenomenological joining of long- and short-distance effects, with a running coupling constant such that g²(k) ～ k^?2 for small k. Spin-dependent potentials have no linearly-rising parts, and there are no strong Van der Waals forces. Little is said about gluon dynamics, except to point out the existence of rather massive hadronic glueballs and of (classically singular) instanton-like solutions which are screened at large distances.     

Quark gluon scattering at higher orders in QCD

The infrared evolution equation which sums up leading logarithmic terms is solved for the partonic reactionqgqX in the elastic case i.e.M _X0. The results of the exactO( _s ³ ) calculation are reproduced.     

QCD真空凝聚和参数化的夸克传播子

基于整体色对称模型,用完全穿衣服参数化的夸克传播子研究了量子色动力学(QCD)真空的性质,预言了各种表征QCD真空的凝聚值.其结果与其他唯象QCD理论模型的预言是一致的.结果清楚地表明了参数化的夸克传播子是成功和可靠的.讨论了计算QCD真空凝聚值时积分截断参数的问题,提出了一个避免计算的结果对截断参数强烈依赖的物理方法.     

Non-perturbative Aspects of QCD and Parameterized Quark Propagator

Based on the Global Color Symmetry Model, the non-perturbative Q, CD vacuum is investigated in the parameterized fully dressed quark propagator. Our theoretical predictions for various quantities characterized the QCD vacuum are in agreement with those predicted by many other phenomenologieal QCD inspired models. The successful predictions clearly indicate the extensive validity of our parameterized quark propagator used here. A detailed discussion on the arbitrariness in determining the integration cut-off parameter ofμ in calculating QCD vacuum condensates and a good method, which avoided the dependence of calculating results on the cut-off parameter is also strongly recommended to readers.     

Dynamical Model of QCD Vacuum and Quark Confinement

The phase transition of a simple local gauge model is investigated in terms of the Nambu-Jona-Lasinio mechanism and it is pointed out that the physical vacuum of QCD is bound state of quark-antiquark pairs which can be viewed, generally, as a nearly perfect color dia-electric medium. An important relation between the vacuum expectation value of gauge fields and scalar fields is also derived by solving the Euler equation for the gauge fields. Based on this relation the SU_C(3) gauge potential is given which can be used to explain the asymptotic behavior and confinement of quarks in a hadron, and at the same time the Yukawa potential of strong interaction can be given too.     

由QCD求和规则计算s夸克质量

简要回顾了量子色动力学求和规则在计算s夸克质量方面的应用.结合Dominguez,Gend和Paver的工作,重新考虑渐近自由阈以下的谱函数后,计算了s夸克的质量,得到s夸克的跑动质量(-m)s(1 GeV)=219 MeV.讨论了影响计算结果精度的可能因素.     

Quark matter nucleation in hot hadronic matter

We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass M_cr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<M_cr could survive the early stages of their evolution without decaying to a quark star.     

非微扰QCD真空中夸克真空凝聚的结构(英文)

基于Dyson-Schwinger方程(DSEs)所确定的夸克传播子和算符成积展开(OPE),在彩虹近似下,预言了QCD真空中非定域夸克真空凝聚的结构。这种结构由夸克自能函数Af和Bf决定,通过数值求解DSEs就可以得到这些自能函数。但是,直接数值求解DSEs方程非常复杂,这里采用Roberts和Williams提出的参数化方法,用参数化的夸克传播函数σf v(p2)和σf s(p2)计算夸克自能函数。同时,也计算了定域的夸克真空凝聚值,夸克胶子混合的真空凝聚值,以及夸克的虚度。理论预言和计算结果均与标准QCD求和定则、格点QCD和瞬子模型的理论结果大致相符。和这些模型的结果相比,参数化方法得到的轻夸克(u,d,s)的定域真空凝聚偏大,这主要是由于模型依赖导致的。与u,d夸克相比,s夸克的真空凝聚比较大,这是因为s夸克自身质量较大的缘故。当然,Roberts-Williams参数化的夸克传播子只是一个经验公式,只能近似描述夸克的传播。     

Constrained effective potential in hot QCD

Constrained effective potentials in hot gauge theory give the probability that a configuration p of the order parameter (Polyakov loop) occurs. They are important in the analysis of surface effects and bubble formation in the plasma. The vector potential appears non-linearly in the loop; in weak coupling the linear term gives rise to the traditional free-energy graphs. But the non-linear terms generate insertions of the constrained modes into the free-energy graphs, through renormalisations of the Polyakov loop. These insertions are gauge dependent and are necessary to cancel the gauge dependence of the free-energy graphs. The latter is shown, through the BRST identities, to have again the form of constrained mode insertions. We stress that the effective action, without this insertion, is gauge variant and gives quite deceptive information. Amongst more it follows, that absolute minima of the potential are at the center group values of the loop, once the insertion is done. We evaluate the two-loop contributions for SU(N) gauge theories, with and without quarks, for the full domain of the N − 1 variables.     

Chasing electric flux in hot QCD

In this talk, I present the status of attempts to analyze the behavior of the so-called spatial 't Hooft loop, which can be taken as an order parameter for the deconfinement phase transition in pure SU(N) gauge theory. While lattice data show a strikingly universal scaling of extracted k–string tensions for various values of k and N, the analytic approach to these observables might need some refinement.     

Tensor Susceptibilities of QCD Vacuum and Parameterized Quark Propagator

Based on the parameterized fully dressed quark propagator proposed by us, the tensor susceptibilities of QCD vacuum and quark vacuum condensates are investigated. Our predicted values of the tensor susceptibilities are in agreement with those predicted by many other theoretical models with QCD feature. The results also show that the tensor susceptibility of QCD vacuum strongly depends on flavor of quark but not sensitive to variation of quark vacuum condensates. However, the quark vacuum condensate is very sensitive to the change of cut-off-parameter μ^2 of the integration, that is, it depends on the separation point of perturbative and non-perturbative QCD region. The successful predictions clearly indicate the extensive validity of our parameterized fully dressed quark propagator used here.     

Quark number susceptibilities: Lattice QCD versus PNJL model

Quark number susceptibilities at finite quark chemical potential are investigated in the framework of the Polyakov-loop-extended Nambu–Jona-Lasinio (PNJL) model. A detailed comparison is performed between the available lattice data, extrapolated using a Taylor expansion around vanishing chemical potential, and PNJL results consistently obtained from a Taylor series truncated at the same order. The validity of the Taylor expansion is then examined through a comparison between the full and truncated PNJL model calculations.     

Multiloop Bubbles for hot QCD

In this article, we present analytical expansion results of two single mass scale four-loop vacuum integrals in d=3−2 dimensions. After finding hypergeometric representations with half-integer coefficients, we use algorithms which we implemented in FORM to expand these in terms of nested sums.     

Quark distributions in QCD sum rules: Unexpected features and paradoxes

Some very unusual features of the hadron structure functions, obtained in generalized QCD sum rules, like the surprisingly strong difference between longitudinally and transversally polarized ρ-meson structure functions and the strong suppression of the gluon sea in the longitudinally polarized ρ meson, are discussed. The text was submitted by the authors in English.     

Gluon Propagator and Heavy Quark Potential in an Anisotropic QCD Plasma

The hard-loop resummed propagator in an anisotropic QCD plasma in general linear gauges are computed. We get the explicit expressions of the gluon propagator in covariant gauge, Coulomb gauge and temporal axial gauge. Considering one gluon exchange, the potential between heavy quarks is defined through the Fourier transform of the static propagator. We find that the potential exhibits angular dependence and that there is stronger attraction on distance scales on the order of the inverse Debye mass for quark pairs aligned along the direction of anisotropy than for transverse alignment.